diff --git a/server/mockfs/mockfs.go b/server/mockfs/mockfs.go
index 2dfd323..8b14ba3 100644
--- a/server/mockfs/mockfs.go
+++ b/server/mockfs/mockfs.go
@@ -20,11 +20,11 @@ import (
 var ErrPathNotFound = errors.New("path not found")
 
 type MockFS struct {
-	t       testing.TB
-	scanner *scanner.Scanner
-	dir     string
-	reader  *mreader
-	db      *db.DB
+	t         testing.TB
+	scanner   *scanner.Scanner
+	dir       string
+	tagReader *tagReader
+	db        *db.DB
 }
 
 func New(t testing.TB) *MockFS                        { return new(t, []string{""}) }
@@ -52,15 +52,15 @@ func new(t testing.TB, dirs []string) *MockFS {
 		}
 	}
 
-	parser := &mreader{map[string]*Tags{}}
-	scanner := scanner.New(absDirs, dbc, ";", parser)
+	tagReader := &tagReader{paths: map[string]*tagReaderResult{}}
+	scanner := scanner.New(absDirs, dbc, ";", tagReader)
 
 	return &MockFS{
-		t:       t,
-		scanner: scanner,
-		dir:     tmpDir,
-		reader:  parser,
-		db:      dbc,
+		t:         t,
+		scanner:   scanner,
+		dir:       tmpDir,
+		tagReader: tagReader,
+		db:        dbc,
 	}
 }
 
@@ -104,11 +104,12 @@ func (m *MockFS) addItems(prefix string, covers bool) {
 		for al := 0; al < 3; al++ {
 			for tr := 0; tr < 3; tr++ {
 				m.AddTrack(p("artist-%d/album-%d/track-%d.flac", ar, al, tr))
-				m.SetTags(p("artist-%d/album-%d/track-%d.flac", ar, al, tr), func(tags *Tags) {
+				m.SetTags(p("artist-%d/album-%d/track-%d.flac", ar, al, tr), func(tags *Tags) error {
 					tags.RawArtist = fmt.Sprintf("artist-%d", ar)
 					tags.RawAlbumArtist = fmt.Sprintf("artist-%d", ar)
 					tags.RawAlbum = fmt.Sprintf("album-%d", al)
 					tags.RawTitle = fmt.Sprintf("title-%d", tr)
+					return nil
 				})
 			}
 			if covers {
@@ -134,8 +135,8 @@ func (m *MockFS) Symlink(src, dest string) {
 	}
 	src = filepath.Clean(src)
 	dest = filepath.Clean(dest)
-	for k, v := range m.reader.tags {
-		m.reader.tags[strings.Replace(k, src, dest, 1)] = v
+	for k, v := range m.tagReader.paths {
+		m.tagReader.paths[strings.Replace(k, src, dest, 1)] = v
 	}
 }
 
@@ -240,15 +241,18 @@ func (m *MockFS) AddCover(path string) {
 	defer f.Close()
 }
 
-func (m *MockFS) SetTags(path string, cb func(*Tags)) {
+func (m *MockFS) SetTags(path string, cb func(*Tags) error) {
 	abspath := filepath.Join(m.dir, path)
 	if err := os.Chtimes(abspath, time.Time{}, time.Now()); err != nil {
 		m.t.Fatalf("touch track: %v", err)
 	}
-	if _, ok := m.reader.tags[abspath]; !ok {
-		m.reader.tags[abspath] = &Tags{}
+	r := m.tagReader
+	if _, ok := r.paths[abspath]; !ok {
+		r.paths[abspath] = &tagReaderResult{tags: &Tags{}}
+	}
+	if err := cb(r.paths[abspath].tags); err != nil {
+		r.paths[abspath].err = err
 	}
-	cb(m.reader.tags[abspath])
 }
 
 func (m *MockFS) DumpDB(suffix ...string) {
@@ -300,19 +304,24 @@ func (m *MockFS) DumpDB(suffix ...string) {
 	}
 }
 
-type mreader struct {
-	tags map[string]*Tags
+type tagReaderResult struct {
+	tags *Tags
+	err  error
 }
 
-func (m *mreader) Read(abspath string) (tags.Parser, error) {
-	parser, ok := m.tags[abspath]
+type tagReader struct {
+	paths map[string]*tagReaderResult
+}
+
+func (m *tagReader) Read(abspath string) (tags.Parser, error) {
+	p, ok := m.paths[abspath]
 	if !ok {
 		return nil, ErrPathNotFound
 	}
-	return parser, nil
+	return p.tags, p.err
 }
 
-var _ tags.Reader = (*mreader)(nil)
+var _ tags.Reader = (*tagReader)(nil)
 
 type Tags struct {
 	RawTitle       string
diff --git a/server/scanner/scanner_fuzz_test.go b/server/scanner/scanner_fuzz_test.go
index 634fbf8..aa833a4 100644
--- a/server/scanner/scanner_fuzz_test.go
+++ b/server/scanner/scanner_fuzz_test.go
@@ -37,7 +37,10 @@ func FuzzScanner(f *testing.F) {
 		for i := 0; i < toAdd; i++ {
 			path := fmt.Sprintf("artist-%d/album-%d/track-%d.flac", i/6, i/3, i)
 			m.AddTrack(path)
-			m.SetTags(path, func(tags *mockfs.Tags) { fuzzStruct(i, data, tags) })
+			m.SetTags(path, func(tags *mockfs.Tags) error {
+				fuzzStruct(i, data, tags)
+				return nil
+			})
 		}
 
 		checkDelta(is, m, toAdd, toAdd) // we added all tracks, 0 delta
diff --git a/server/scanner/scanner_test.go b/server/scanner/scanner_test.go
index a10588b..5d812b1 100644
--- a/server/scanner/scanner_test.go
+++ b/server/scanner/scanner_test.go
@@ -111,11 +111,12 @@ func TestUpdatedTags(t *testing.T) {
 	defer m.CleanUp()
 
 	m.AddTrack("artist-10/album-10/track-10.flac")
-	m.SetTags("artist-10/album-10/track-10.flac", func(tags *mockfs.Tags) {
+	m.SetTags("artist-10/album-10/track-10.flac", func(tags *mockfs.Tags) error {
 		tags.RawArtist = "artist"
 		tags.RawAlbumArtist = "album-artist"
 		tags.RawAlbum = "album"
 		tags.RawTitle = "title"
+		return nil
 	})
 
 	m.ScanAndClean()
@@ -127,11 +128,12 @@ func TestUpdatedTags(t *testing.T) {
 	is.Equal(track.Album.TagTitle, "album")                                                                     // track has tags
 	is.Equal(track.TagTitle, "title")                                                                           // track has tags
 
-	m.SetTags("artist-10/album-10/track-10.flac", func(tags *mockfs.Tags) {
+	m.SetTags("artist-10/album-10/track-10.flac", func(tags *mockfs.Tags) error {
 		tags.RawArtist = "artist-upd"
 		tags.RawAlbumArtist = "album-artist-upd"
 		tags.RawAlbum = "album-upd"
 		tags.RawTitle = "title-upd"
+		return nil
 	})
 
 	m.ScanAndClean()
@@ -234,10 +236,10 @@ func TestGenres(t *testing.T) {
 	}
 
 	m.AddItems()
-	m.SetTags("artist-0/album-0/track-0.flac", func(tags *mockfs.Tags) { tags.RawGenre = "genre-a;genre-b" })
-	m.SetTags("artist-0/album-0/track-1.flac", func(tags *mockfs.Tags) { tags.RawGenre = "genre-c;genre-d" })
-	m.SetTags("artist-1/album-2/track-0.flac", func(tags *mockfs.Tags) { tags.RawGenre = "genre-e;genre-f" })
-	m.SetTags("artist-1/album-2/track-1.flac", func(tags *mockfs.Tags) { tags.RawGenre = "genre-g;genre-h" })
+	m.SetTags("artist-0/album-0/track-0.flac", func(tags *mockfs.Tags) error { tags.RawGenre = "genre-a;genre-b"; return nil })
+	m.SetTags("artist-0/album-0/track-1.flac", func(tags *mockfs.Tags) error { tags.RawGenre = "genre-c;genre-d"; return nil })
+	m.SetTags("artist-1/album-2/track-0.flac", func(tags *mockfs.Tags) error { tags.RawGenre = "genre-e;genre-f"; return nil })
+	m.SetTags("artist-1/album-2/track-1.flac", func(tags *mockfs.Tags) error { tags.RawGenre = "genre-g;genre-h"; return nil })
 	m.ScanAndClean()
 
 	isGenre("genre-a") // genre exists
@@ -257,7 +259,7 @@ func TestGenres(t *testing.T) {
 	isAlbumGenre("artist-0/", "album-0", "genre-a") // album genre exists
 	isAlbumGenre("artist-0/", "album-0", "genre-b") // album genre exists
 
-	m.SetTags("artist-0/album-0/track-0.flac", func(tags *mockfs.Tags) { tags.RawGenre = "genre-aa;genre-bb" })
+	m.SetTags("artist-0/album-0/track-0.flac", func(tags *mockfs.Tags) error { tags.RawGenre = "genre-aa;genre-bb"; return nil })
 	m.ScanAndClean()
 
 	isTrackGenre("artist-0/", "album-0", "track-0.flac", "genre-aa")       // updated track genre exists
@@ -325,11 +327,12 @@ func TestNewAlbumForExistingArtist(t *testing.T) {
 
 	for tr := 0; tr < 3; tr++ {
 		m.AddTrack(fmt.Sprintf("artist-2/new-album/track-%d.mp3", tr))
-		m.SetTags(fmt.Sprintf("artist-2/new-album/track-%d.mp3", tr), func(tags *mockfs.Tags) {
+		m.SetTags(fmt.Sprintf("artist-2/new-album/track-%d.mp3", tr), func(tags *mockfs.Tags) error {
 			tags.RawArtist = "artist-2"
 			tags.RawAlbumArtist = "artist-2"
 			tags.RawAlbum = "new-album"
 			tags.RawTitle = fmt.Sprintf("title-%d", tr)
+			return nil
 		})
 	}
 
@@ -351,20 +354,22 @@ func TestMultiFolderWithSharedArtist(t *testing.T) {
 	const artistName = "artist-a"
 
 	m.AddTrack(fmt.Sprintf("m-0/%s/album-a/track-1.flac", artistName))
-	m.SetTags(fmt.Sprintf("m-0/%s/album-a/track-1.flac", artistName), func(tags *mockfs.Tags) {
+	m.SetTags(fmt.Sprintf("m-0/%s/album-a/track-1.flac", artistName), func(tags *mockfs.Tags) error {
 		tags.RawArtist = artistName
 		tags.RawAlbumArtist = artistName
 		tags.RawAlbum = "album-a"
 		tags.RawTitle = "track-1"
+		return nil
 	})
 	m.ScanAndClean()
 
 	m.AddTrack(fmt.Sprintf("m-1/%s/album-a/track-1.flac", artistName))
-	m.SetTags(fmt.Sprintf("m-1/%s/album-a/track-1.flac", artistName), func(tags *mockfs.Tags) {
+	m.SetTags(fmt.Sprintf("m-1/%s/album-a/track-1.flac", artistName), func(tags *mockfs.Tags) error {
 		tags.RawArtist = artistName
 		tags.RawAlbumArtist = artistName
 		tags.RawAlbum = "album-a"
 		tags.RawTitle = "track-1"
+		return nil
 	})
 	m.ScanAndClean()
 
@@ -425,11 +430,12 @@ func TestSymlinkedSubdiscs(t *testing.T) {
 	addItem := func(prefix, artist, album, disc, track string) {
 		p := fmt.Sprintf("%s/%s/%s/%s/%s", prefix, artist, album, disc, track)
 		m.AddTrack(p)
-		m.SetTags(p, func(tags *mockfs.Tags) {
+		m.SetTags(p, func(tags *mockfs.Tags) error {
 			tags.RawArtist = artist
 			tags.RawAlbumArtist = artist
 			tags.RawAlbum = album
 			tags.RawTitle = track
+			return nil
 		})
 	}